GMS was Japan's first national satellite program for weather and environmental observations from GEO (Geostationary Earth Orbit). It was administered in partnership by JMA (Japan Meteorological Agency) as the operator of the satellites, and by JAXA (formerly NASDA) as the spacecraft and launch service provider (originally, NASDA was also the spacecraft operator). In Japan, the GMS program was also known by the name of Himawari (sunflower). The GMS program called for one operational spacecraft in orbit on the basis of a continuous service provision for the series. The operational meteorological program series consisted of the following satellites:

Observation/service coverage of GMS program. Meteorological data is provided for the Asia-Pacific Region which includes Japan, Australia, parts of China, Korea, and Oceania (Burma, Indonesia, Laos, Malaysia, Mongolia, New Zealand, the Philippines, Taiwan, Thailand, Tibet, and Vietnam). The VISSR imagery coverage extends roughly from ±60º in latitude and from 80º E to 160 W in longitude. In addition, the GMS satellite data represent an important link and an integral part in the WWW (World Weather Watch) program, sponsored by the World Meteorological Organization (WMO).

All GMS spacecraft were built for JAXA (former NASDA) by BSS [Boeing Satellite Systems - the former Hughes Space and Communications Company (HSC)], El Segundo, CA, in close cooperation with NEC (Nippon Electric Company) Corporation of Tokyo (NEC was actually the prime contractor to NASDA). The development of the GMS series relied heavily on the early US GOES series design.

All GMS spacecraft are spin-stabilized. The GMS-5 satellite has a launch mass of 725 kg (satellite diameter = 214.6 cm, height = 345 cm); the on-orbit mass is 344 kg at BOL. The spacecraft consists of a despun Earth-oriented antenna assembly and a spinning section rotating at 100 rpm. The observation payload and its supporting subsystems are part of the spinning section of the spacecraft. Attitude information is provided by Earth horizon and sun sensors. Solar cells applied to the exterior of the spacecraft bus generate up to 300 W of power. The design life is 5 years. Hydrazine thrusters maintain the desired geostationary position and counteract perturbations attempting to alter the vehicle's inclination. 1)2)3)4)

The helical antenna in UHF band is used for the reception of the DCP data and S&R signals and the transmission and reception of Tsunami warnings. The omni-directional antenna in S-band is used for TT&C (Tracking Telemetry and Command). The despun-controlled parabolic antenna in S-band is used for the transmission of the VISSR raw data, the dissemination of S-VISSR and WEFAX, the transmission of DCP data and S&R signals as well as TT&C including the trilateral ranging.

The GMS satellite series is being operated by the MSC (Meteorological Data Center) of JMA.

Figure 2: GMS series satellites (image credit: BSS)

Sensor complement: (VISSR, SEM, DCS)

VISSR (Visible and Infrared Spin-Scan Radiometer):

VISSR was built by former Hughes SBRC (Santa Barbara Research Center), now Raytheon SBRS (Santa Barbara Remote sensing). VISSR consists of the following elements: an optical telescope with a scan mirror, reflectors and lenses, together with the visible (VIS) and infrared (IR) detectors and the radiation cooler. The optical axis of VISSR is in line with the spacecraft mechanical centre axis. The spinning motion allows the VISSR to scan the earth scene west-to-east, one scan during each revolution.

The VISSR is used to obtain visible and infrared spectrum mappings of the Earth and its cloud cover. Four photomultiplier tube detectors (PMTs) and redundant sets convert the visible spectra into four-channel analog signals. A cooled (95 K) HgCdTe detector (also redundant) converts infrared spectra into an infrared signal (10.5-12.5 µm) at 5 km resolution. The resulting data stream is then fed into the VISSR Digital Multiplexer (VDM) unit.

Figure 3: Schematic of the VISSR instrument (image credit: JMA)

For the GMS-5 mission, the VISSR instrument received an additional water vapor channel (6.5 - 7.0 µm); furthermore, the original infrared channel was split into two channels (10.5 - 11.5 and 11.5 - 12.5 µm). The visual sensor array of 4 sensors captures an image of 13376 x 10000 pixels with 6 bit data quantization. Each of the infrared sensors captures an image of 6688 x 2500 pixels with 8 bit depth.

The DCS on-board GMS provides a transponder with a passband that is divided into 133 communication channels separated at intervals of 3 kHz. The system has the ability of simultaneous communication through all channels. The 133 channels are divided into two blocks: 100 are for regional use, and 33 are for international use. Each DCP is allocated one of the 133 parallel channels. Since the DCPs transmit either according to a schedule, or under `alert' conditions, many platforms can use a single 3 kHz channel sequentially. A message from a DCP in the ground segment is relayed via the GMS on-board DCS to a ground-based MSC which is responsible for the coverage area. - The platforms (DCPs) transmit (uplink) their data in the 402 MHz UHF band to the GMS on-board DCS, where it is converted to S-band (1694 MHz) and retransmitted (downlinked) to a ground facility CDAS (Command and Data Acquisition Station) and relayed via GTS to MSC. There, the DCP messages are collected, processed, disseminated, formatted into bulletins and distributed via GTS to the platform owners.

As of the end of 1995, 448 DCPs in the ground segment are regularly serviced by GMS. The DCPs which can be operated by the system are of two types:

• self-timed DCPs which transmit their data automatically at preset time slots driven by an internal stable clock

• interrogational DCPs which transmit their data only when an interrogation command is received at the DCP.

The GMS DCS is part of an international network in the framework of WWW (together with Meteosat and GOES series satellites); this allows a further classification:

• International DCPs (IDCPs) which are mobile (Lagrangian type free-floating in the medium) and whose data may be collected by any one of the satellite operators. The allocated frequency band for the IDCP operation is 402.0-402.1 MHz for the uplink and 1694.3-1694.4 MHz for the downlink.

• Regional DCPs (RDCPs) which are under the responsibility of and operated by a specific satellite operator. The allocated frequency band for the RDCP operation is 402.1 - 402.4 MHz for the uplink and 1694.4 - 1694.7 MHz for the downlink.

Background: GMS-5, with a design life of 5 years, was due to be replaced by a satellite called MTSAT (Multifunction Transport Satellite) in November 1999; however, the launch vehicle (H-II) for MTSAT failed and the satellite was destroyed. This mishap implied an immediate new order and manufacturing start for a replacement of MTSAT. In addition, significant efforts to extend the usable life of GMS-5 were implemented by JMA in July 2001, so that it operated for more than 3 years beyond its design life.

JMA negotiated with NOAA, the US National Oceanic & Atmospheric Administration, for GOES-9 to be moved over the Western Pacific to provide images in place of the ailing GMS-5 spacecraft until the launch of replacement. The replacement is a new Japanese satellite called MTSAT-1R (Multifunction Transport Satellite-1 Replacement), which is expected to become operational in 2005. - GOES-9, also launched in 1995, was removed by NOAA from operational service in July 2002, because it did not meet anymore US weather forecasting requirements. But GOES-9 still did have sounding and limited imaging capabilities which could supply data comparable to that of the GMS-5 spacecraft.

In May 2002, NOAA announced that the US had agreed to lend Japan a geostationary environmental satellite to ensure that weather data from the Western Pacific are available continuously should the weakening Japanese satellite fail. GOES-9 could be placed in an orbit over the Western Pacific region. - In April 2003, GOES-9 assumed its new GEO position at 155º E. 7)

• In April/May 2003, JMA started backup operations of GMS-5 with the GOES-9 spacecraft, in cooperation with NOAA/NESDIS.

• GMS-5 made its final observation at 00 UTC on 22 May 2003.

• A launch of MTSAT-1R took place on Feb. 26, 2005.

• On June 28, 2005, the geostationary meteorological satellite of Japan was switched over from GOES-9 to Himawari-6 (MTSAT-1R). 8)

Parameter

GMS-5

GOES-9

Visible VIS
Resolution; quantization

0.50-0.75 µm
1.25 km; 6 bit

0.55-0.75 µm
1 km; 10 bit

Thermal Infrared 1 (TIR1)
Resolution, quantization

10.5-11.5 µm
5 km; 8 bit

10.2-11.2 µm
4 km; 10 bit

Thermal Infrared 2 (TIR2)
Resolution; quantization

11.5-12.5 µm
5 km; 8 bit

11.5-12.5 µm
5 km, 8 bit

Infrared 3 (water vapor)
Resolution; quantization

6.5-7.0 µm
5 km; 8 bit

6.5-7.0 µm
8 km; 10 bit

Shortwave Infrared (SWIR)
Resolution; quantization

-

3.8-4.0 µm
4 km; 10 bit

S/C location

140º E

155º E

Table 5: Spectral parameter comparison of GMS-5 and GOES-9

Figure 5: Overview of the Japanese meteorological satellite series (image credit: JMA) 9)10)

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.